There are several factors that are potentially relevant to the design and performance of orthopaedic implants. In the example of a tibial tray, a non-exhaustive list of such factors includes the implant's flexibility (or the flexibility of certain portions of the implant or its flexibility about certain axes or other constructs), which may indicate the degree to which the tray will conform to the potentially uneven resected surfaces of a proximal tibia; the implant's rigidity (or the rigidity of certain portions of the implant or its rigidity about certain axes or other constructs), which may indicate the degree to which stresses or other forces imposed by the bony and other anatomy associated with the knee joint will be transmitted to the peripheral hard cortical shell of the proximal tibia; the implant's resistance to rotation; the amount of bone preserved; and/or other potentially relevant factors. In some instances, accommodation of these or other factors may require trade-offs to balance competing factors. In some instances, one or more of these factors will not be considered or given a high level of importance to the design of an orthopaedic implant.
Some known tibial trays include a fin or a keel that may increase the strength of the implant while also helping to prevent rotation relative to the bone. In some instances, such fins or keels may present certain drawbacks. For instance, in some cases, the fin or keel may impede the visualization of the implant and surrounding anatomy using x-ray or other imaging technologies. For instance, it may be desirable in some cases to visualize the implant and its surrounding anatomy, including the surrounding bony anatomy, by taking one or more x-rays in planes such as coronal and sagittal planes or in other planes to assess whether the implant may be loosening over time. Such loosening might be indicated by lucent lines appearing in the x-ray image around portions of the implant or other indications that the bone has receded from the implant or otherwise has become loose. In some instances, a fin or keel of the implant may obstruct the ability to view such lucent lines or may otherwise hinder the evaluation of the image. Other orthopaedic components might feature these or other structures similarly impairing visualization of the implant in the bone and other anatomy.
Some known tibial trays are difficult to remove or revise. For some revision procedures, it is necessary to cut around the existing implant or otherwise position instrumentation about the implant to loosen it from the surrounding bone and/or other anatomy before removal. In some instances, particularly, for instance, some instances where the implant is a tibial tray having a keel, it may be difficult to cut around certain portions of the keel or otherwise access certain areas of the bone-implant interface to loosen the implant. It may be particularly difficult, for instance, to access certain areas of the bone-implant interface depending on the surgical approach taken. For instance, if an anterior-medial incision is used to access the knee joint, the keel structure may impede a surgeon's access to posterior-lateral portions of the bone-implant interface. In such instances, removal of the implant may undesirably require excessive or unintended bone removal as well.
In some instances, stability or fixation of the implant, such as a tibial tray or other implant, in the bone may be of some significance. For instance, the distribution of “hard” versus “soft” bone is not always uniform or predictable, and, in some instances, during bone preparation a punch, drill or other instrument may penetrate the bone at an undesired angle or position since it may tend to follow the path of least resistance into softer bone. Moreover, in some instances, such as some tibial cases, distal metaphyseal bone may tend to be spongier and softer than proximal metaphyseal bone. In some implant cases, it may be difficult to achieve adequate fixation or other stability in the distal metaphyseal bone. Moreover, with some implants, including some tibial implants, there may be a tendency over time for the implant to subside or migrate.